Kate McCann has opened her heart about how she felt like committing suicide in the days after her daughter Madeleine vanished from their apartment in Portugal four years ago.

Madeleine was three years old when she was abducted, having been left alone with her brother and sister, Sean and Amelie, while their parents dined with friends nearby.

Her mother realised she had been taken as she made the latest of a series of half-hourly checks.

In a new book to mark the fourth anniversary of her daughter's disappearance, Mrs McCann recalls running outside, screaming: "Madeleine's gone! Someone's taken her!"

Later, she sank into fits and anguish and depression that eventually threatened to destroy her relationship with her husband, Gerry.

She writes: "I had an overwhelming urge to swim out across the ocean, as hard and as fast as I could; to swim and swim and swim until I was so far out and so exhausted I could just allow the water to pull me under and relieve me of this torment.

"Somehow, inflicting physical pain on myself seemed to be the only possible way of escaping my internal pain. The other truly awful manifestation of what I was feeling was a macabre slide show of vivid pictures in my brain that taunted me relentlessly.

"I was crying out that I could see Madeleine lying, cold and mottled, on a big grey stone slab. Looking back, seeing me like this must have been terrible for my friends and relatives, particularly my parents, but I couldn't help myself."

She said that she was stuck in an "endless bad dream" and haunted by visions of her missing daughter Madeleine after her disappearance.

Visions

Mrs McCann described how she immediately feared that the youngster had fallen victim to a paedophile.

The 43-year-old said: "The pictures I saw of our Madeleine no sane human being would want in her head, but they were in mine."

In another extract, Mrs McCann revealed that her husband was also wracked with similar harrowing visions.

Mrs McCann wrote: "I asked Gerry apprehensively if he'd had any any really horrible thoughts or visions of Madeleine.

"He nodded."

Mrs McCann, from Rothley, Leicestershire, also lays bare how she wanted to kill and "inflict the maximum pain possible" on the person who had abducted her daughter.

The book also criticises the Portuguese authorities, who shelved the investigation into Madeleine's disappearance in July 2008, for failing to investigate other alleged child abductions thoroughly.

The McCanns hope that the publication will prompt people holding vital information about what happened to the child to come forward at last.